J. K. Rowling is the only major fantasy English-language fantasy writer to have completely saturated the market with merchandise described in her books: her imagination is naturally commodifying. Diana Wynne Jones wrote more books revolving around magical powers, but the plots and characters are not contained in one world. There are seven volumes by Ursula K. Le Guin about the great archipelago of Earthsea, where wizards and ordinary people live frugally without the assistance of technology or pleasures of many creature comforts. Things are central to the imaginative realm of Rowling in a way they never were in those of Wynne Jones and Le Guin. Say “Harry Potter” and chances are a product she dreamed up as likely to pop into your head; there is no comparable reaction when hearing “Chrestomanci” or “Sparrowhawk.”
Only those immersed in the Harry Potter series as youngsters will put on their bucket list a visit to Platform 9 ¾, the flagship of official licensed Harry Potter shops in King’s Cross Station. Somewhere among the wizarding world collectibles for Muggles may be found for that petite madeleine—or rather Bertie Bott’s Every-Flavour Beans—that will keep the memories ever green of reading the books, listening to the audio-recordings, and watching the films. A jar of Bobotuber pus cannot be had there for love or money, but there is more than enough swag to cram full an expandable bag. A set of Horcruxes? An LGBT pride tee shirt? A Divination tea set? A Gringotts bank? A Final Challenge chess set? What will you have?
It’s even possible to imagine Rowling’s characters visiting Platform 9 ¾ as a shadowy simulacrum of Diagon Alley. Draco would stalk down the aisles looking for merch from the dark side— the Death Eaters’ masks or the movie prop replica of his wand authenticated by Warner Brothers in an Ollivander’s box plus a Slytherin wand stand—that might stir his pure blood and uncurl his lip very slightly.
Ron would deny the existence of knock-offs of his mother’s infamous Christmas sweaters. Being chronically short of pocket money, he would have to be contented with picking up some cheap Quidditch memorabilia or trying to complete his set of chocolate frog wizard cards.
There isn’t anything quirky enough in the shop to catch Luna’s eye. If witches used mobile phones, she could search Etsy for unique items like customized cake decorations, a polymer clay statue of Dobby and the sock that liberated him, or a full-scale model of Harry’s cupboard while waiting for her friends to finish browsing. The attempts to copy her personal style, on the other hand, she might not take as a compliment, even if the prices were reasonable.
What about Hermione? It’s hard to imagine her wearing a charm bracelet with miniatures of the winged key or the Tri-wizard Tournament cup. But the best witch of her generation can’t resist a good reference book, so she might just not be able to resist a copy of the Unofficial Harry Potter Character Compendium compiled by Mugglenet bound in “premium leather accented in true 22K gold” from Easton Press for $147.00 (payment in three convenient installments is also an option). 
And her preference for books is, surprisingly enough, the soundest in terms of investment value. The books that started the tsunami of authorized merchandise, have held their value relative to the tchotchkes: thousands of dollars separate the priciest lots of merch on EBay from the seven titles in the series. Buying a first edition of Harry Potter and the Goblet of Fire on Ebay would be foolhardy, given the very brief descriptions posted there, but armed with Phillip W. Errington’s updated edition of J. K. Rowling: A Bibliography (London: Bloomsbury Academic, 2015), I can examine any copy at hand and be confident of identifying one of the several million copies of the first printing of the American edition. In fact, there’s one in my basement, but it’s been handled too much to realize full market value. Pity.
Errington succeeds in bestowing upon Rowling’s body of writing literary legitimacy, but fails to give any indication of the existence of the parallel collecting universe she has authorized to extend the wizarding world’s reach far beyond the printed page. Legions of devout fans haunt Ebay for Harry Potter memorabilia because it’s affordable. It can be bought in lots sold by weight or acquired painstakingly item by item. For a Hagrid completist, it would be necessary to track down all forms of Fang, Fluffy, Norbert, Buckbeak, Blast-ended skrewts, Aragog, etc. Having gone that far down the path to the Forbidden Forest, the passionate collector would then be obligated to add all the different versions of his hut (that’s a lot of Legos) and the peculiar objects inspired by the birthday cake he baked for Harry…. 
All this activity raises the dementors of storage versus display–and either option eats up space and tests the forbearance of loved ones. It has even wider ramifications. Best-selling books may be the heart and soul of any campaign to exploit their commercial potential as a beloved cultural property, but overlooking all the merch (however sane a decision it may be on the bibliographer’s part) fails to come to terms with the cataclysmic changes marketing and branding have wrought in the literary landscape of late twentieth and early twenty first centuries. To understand the impact of Rowling’s imagination, it is important to take into account her fans’ powerful desire to acquire solid, displayable, wearable tokens of the wizarding world.
Read the two articles below for different takes on collecting Harry Potter:
https://hobbyhelp.com/harry-potter-collecting/
